What did @onehottrail actually say?
The creator credits Dr. Jason Fung's fasting approach with helping someone named Hermes Essinic triple his testosterone alongside a 70-pound weight loss. But they're careful to separate the mechanism: they argue the testosterone gains came from "being in a caloric deficit" facilitated by fasting, not from fasting itself. They also claim fasting upregulates the adrenal glands, but say this raises cortisol and actually suppresses gonadal testosterone production. So the video is essentially a partial debunk of someone else's claim, dressed up as a success story.
To their credit, they do not say fasting is a testosterone booster in healthy men. They explicitly state that "if you are healthy slash underweight, fasting has consistently shown to decrease testosterone levels in natural males." That's a meaningful distinction most fitness influencers skip entirely.
Does the science back this up?
Mostly, yes. The core claim that obesity suppresses testosterone is well-established, and weight loss reliably raises levels in hypogonadal obese men. The fasting-cortisol-testosterone mechanism they describe is real but more nuanced than they let on.
A 2012 study by Grossmann in the European Journal of Endocrinology confirmed that obesity-related hypogonadism is largely reversible with significant weight loss. The suppression happens through multiple pathways: elevated estrogen from aromatization in adipose tissue, leptin resistance, and hypothalamic-pituitary-gonadal axis blunting. Losing 70 pounds would plausibly produce a large testosterone increase in someone who was clinically obese, potentially including a tripling if baseline levels were severely suppressed.
On fasting and cortisol: Dutheil et al. (2021, Nutrients) found that intermittent fasting does increase cortisol acutely. And cortisol does suppress LH pulsatility and Leydig cell function, which would reduce testosterone output. The creator's direction of effect is correct here.
What did they get wrong (or right)?
They got the big picture right. Obesity suppresses testosterone, weight loss restores it, and fasting is a vehicle for the caloric deficit rather than a direct hormonal lever in healthy men. That's a defensible, evidence-grounded position.
Where it gets sloppy: the claim that fasting "upregulates the adrenal glands" is an oversimplification. Cortisol elevation during fasting is more accurately a stress response to caloric restriction and glucose availability, not a structural upregulation of adrenal capacity. Calling it "upregulation" implies a lasting adaptation that the evidence does not clearly support for short-term fasting protocols.
Also unaddressed: the magnitude of the claim. "Tripling" testosterone is extraordinary. A man going from 200 ng/dL to 600 ng/dL is plausible after massive weight loss. But the creator presents this as a general outcome without any labs, baseline data, or clinical verification. Anecdote is not evidence, even when the underlying mechanism is biologically plausible.
What should you actually know?
If you are overweight and your testosterone is low, losing a significant amount of body fat is one of the few interventions with consistent clinical support for raising testosterone naturally. A 2013 study by Camacho et al. in the European Journal of Endocrinology found that a 10% reduction in body weight was associated with meaningful testosterone increases in obese men.
Fasting as a tool for achieving that deficit is not inherently harmful to testosterone in this population, but it is not the mechanism. Lean men who fast aggressively may actually see testosterone suppression. Casto and Cunningham (2012, Hormones and Behavior) showed caloric restriction lowers LH and testosterone in non-obese males.
- Testosterone does not triple in healthy, lean men from fasting alone.
- Weight loss is the active ingredient, not the fasting protocol itself.
- Cortisol elevation from fasting can suppress testosterone production at the gonadal level.
- If your testosterone is low, get labs before attributing it to lifestyle or changing anything based on influencer content.
Bottom line
This video is more accurate than most testosterone content on Instagram, and the creator deserves credit for separating correlation from mechanism. But the framing still leans on a dramatic personal anecdote to sell a point, and the adrenal "upregulation" language is imprecise in ways that matter. If you are working with a clinician on hormone optimization, this video would not steer you badly, but it is not a substitute for labs and a diagnosis.